[fsp] Use types from another namespaces in IDL.

chrome/common/extensions/api/file_system_provider_internal.idl

Index: chrome/common/extensions/api/file_system_provider_internal.idl
diff --git a/chrome/common/extensions/api/file_system_provider_internal.idl b/chrome/common/extensions/api/file_system_provider_internal.idl
index 7042897d5244e99a4a2cda16579c4be9360f74c0..1dbeb1c7cc9e6fae346806a870638fbea406be1a 100644
--- a/chrome/common/extensions/api/file_system_provider_internal.idl
+++ b/chrome/common/extensions/api/file_system_provider_internal.idl
@@ -18,9 +18,7 @@ namespace fileSystemProviderInternal {
     static void unmountRequestedError(
         long fileSystemId,
         long requestId,
-        // TODO(mtomasz): Use FileSystemProvider::ProviderError when namespaces
-        // are fully implemented in IDL.
-        DOMString error);
+        fileSystemProvider.ProviderError error);
   };
 };